Ostrich eggshell beads reveal 50,000-year-old social network in Africa

Humans evolved in a patchwork of semi-connected populations across Africa; understanding when and how these groups connected is critical to interpreting our present-day biological and cultural diversity. Genetic analyses reveal eastern and southern African lineages diverged sometime in the Pleistocene, ~350-70 thousand years ago (ka), however, less is known about the exact timing of these interactions, the cultural context of these exchanges, or the mechanisms that drove their separation. Ostrich eggshell (OES) beads are the oldest fully manufactured beads, and could be key to revealing Late Pleistocene social dynamics in Africa. Here, we use OES bead styles as a means to reconstruct population interactions over the past 50,000 years in eastern and southern Africa. We find that OES bead technology likely originated in eastern Africa by 50ka, and spread southward via a regional network. This long-distance connection breaks down by 33ka, as precipitation decreases in eastern Africa. At this time, the Zambezi River catchment (the region connecting eastern and southern Africa) experienced enhanced rainfall and periodic flooding. Together, the timing of these events suggest that climate could be an important mechanism for driving cultural isolation in the Late Pleistocene. Further, the distinct trajectories of bead characteristics suggest that populations in each region responded to environmental changes with different social strategies. Eastern African populations may have sustained larger sizes or most robust social networks, while southern populations could have dispersed into smaller groups with less need for symbolic behavior. Our study reveals intermittent connections between eastern and southern African populations over the past 50ka, implies a later regional divergence than predicted by genetic analyses, and offers important new insights into behavioral responses to climate change.